Tumor cells are known to express antigenic proteins which are intrinsic to the particular type of tumor cells (hereinafter sometimes referred to as a “tumor-associated antigens”). Attempts have been made to develop new therapies for treating tumors by targeting tumor-associated antigens. Monoclonal antibodies that elicit an antigen-antibody response specific to such tumor-associated antigens are known to induce various types of in vivo immune responses (antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), etc.) to attack cancer cells, thereby inducing cell death. Monoclonal antibodies useful for tumor treatment have been developed.
However, the range of monoclonal antibodies useful for tumor treatment is limited. The monoclonal antibodies presently available are capable of treating only a few types of tumors including metastatic breast cancer, acute leukemic myelosis, intractable chronic lymphoma, non-Hodgkin's lymphoma, and multiple myeloma. Development of monoclonal antibodies applicable to treatment of other tumors is desirable.
To obtain a monoclonal antibody useful for tumor treatment, it is necessary to identify a protein specifically expressed in a tumor cell and obtain a monoclonal antibody against this protein antigen.
Human oculospanin protein was obtained as an Expressed Sequence Tag (EST) clone derived from a gene expressed on the retinal pigment epithelium and the ocular choroidal membrane (Molecular Vision (2002) 8, 25-220). The human oculospanin gene has an open reading frame of 1068 bp. Human oculospanin consists of 355 amino acids and is estimated to have a molecular weight of 36.4 kDa based on the DNA sequence. However, the relationship between human oculospanin and tumors is still unknown.